In the fabrication of a semiconductor wafer, as well as in the production of elements, such as reticles, used in the fabrication, there are typically a large number of steps. Each of these steps is time-consuming, and for efficient fabrication it is important to minimize the time taken while maintaining the quality of the steps. For example, in inspecting the wafer during or at conclusion of the fabrication, a number of methods for minimizing the inspection time are known in the art.
Inspection may be performed by scanning the wafer with an electromagnetic wave beam, and observing properties of the beam after it has interacted with the wafer, typically with the wafer surface. Typically the beam is used to generate an image of the wafer surface. The scanning and/or imaging inspection time may be reduced by using multiple inspection beams, each beam having generally similar properties. The beams are focused onto the wafer surface, and are scanned across the surface in tandem. Using a multiplicity of inspection beams produces a corresponding saving in time to scan and/or image the wafer surface, compared to the time taken if only a single beam is used.
PCT Application WO 03/040709, to Almogy, et al., whose disclosure is incorporated herein by reference, describes an optical imaging system which uses a plurality of optical beams from a spot grid array, the beams being focused onto the surface of a wafer. The wafer is moved so that the focused spots continuously and linearly traverse the surface. The spots are offset relative to each other so that the traversed lines followed by adjacent spots do not overlap, but do touch each other. One scan of the array thus images a relatively large swathe of the wafer.